MatrixPlot 1.2: MP format

The mp (matrix plot) format is also a column format. The identifiers (first
word in a line) can either be R, B, I, and M. The "R" line provide the range
(in horizontal and vertical directions) of the matrix plot. Four numbers are
used: xstart, xend, ystart; "B" lines encode for the bars along the edges (max
two); "I" lines encode for the sequence logo profile along the edges; "M" lines
encode for the 2D positions in the matrix plot along with a value that is
represented by a color on the plot. The first column in I and B lines must
always indicate the position in sequence (alignment). In I lines the two
following numbers must be the value of the sequence information and the
frequency of gaps. The B lines can have arbitrarily many columns, but normally
only the two first are used, either to encode a graphical bar (by numbers that
correspond to colors) or by the text string given. However, all the columns of
the B lines can be combined to one string that can be displayed along the edges
of the matrixplot. The numbers that can be used for a bar are 0,1,...,8. These
have fixed rgb values. Two examples are given below, a mutual
information example and a distance matrix example.